U.S. patent application number 12/359533 was filed with the patent office on 2009-05-28 for elastomer composition having glass micro fibers.
Invention is credited to Jesse J. Arnold, Brian R. Bergman.
Application Number | 20090133793 12/359533 |
Document ID | / |
Family ID | 39136206 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090133793 |
Kind Code |
A1 |
Bergman; Brian R. ; et
al. |
May 28, 2009 |
ELASTOMER COMPOSITION HAVING GLASS MICRO FIBERS
Abstract
Elastomer compositions and products formed therefrom, the
compositions including one or more elastomers and glass microfibers
having an average fiber diameter of no more than about 5 .mu.m and
an average length of between about 5 and 200 .mu.m, wherein the
glass microfibers are directionally oriented within the elastomer
composition. Alternatively, the average length of the glass
microfibers may be between 5 and 100 .mu.m or in other embodiments,
between about 10 and 70 .mu.m. The elastomer compositions may be
used to form products that include a tire tread or a support member
within the sidewall of a tire. The glass microfibers may be
oriented in, inter alia, a substantially circumferential
orientation, a tread thickness orientation or at a 45.degree.
orientation in a plane formed between the tread thickness and
circumferential orientations or in a sidewall thickness
direction.
Inventors: |
Bergman; Brian R.;
(Clermont-Ferrand, FR) ; Arnold; Jesse J.;
(Simpsonville, SC) |
Correspondence
Address: |
MICHELIN NORTH AMERICA, INC.;INTELLECTUAL PROPERTY DEPARTMENT
MARC BLDG 31-2, 515 MICHELIN ROAD
GREENVILLE
SC
29605
US
|
Family ID: |
39136206 |
Appl. No.: |
12/359533 |
Filed: |
January 26, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/US06/34065 |
Aug 31, 2006 |
|
|
|
12359533 |
|
|
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Current U.S.
Class: |
152/458 ;
152/525; 523/152 |
Current CPC
Class: |
C08J 2307/00 20130101;
B60C 17/0018 20130101; B60C 11/14 20130101; C08K 7/14 20130101;
B82Y 30/00 20130101; C08K 9/06 20130101; Y10T 152/10513 20150115;
C08K 2201/011 20130101; C08J 2321/00 20130101; B60C 1/0016
20130101; B60C 17/0009 20130101; C08J 5/043 20130101; B60C 1/0025
20130101; B60C 11/00 20130101; C08K 7/14 20130101; C08L 21/00
20130101; C08K 9/06 20130101; C08L 21/00 20130101 |
Class at
Publication: |
152/458 ;
523/152; 152/525 |
International
Class: |
B60C 13/00 20060101
B60C013/00; C08J 5/14 20060101 C08J005/14; B60C 1/00 20060101
B60C001/00 |
Claims
1. An elastomer composition, comprising: an elastomer selected from
one or more natural rubbers, one or more synthetic rubbers or
combinations thereof; glass microfibers having an average fiber
diameter of no more than about 5 .mu.m and an average length of
between about 5 and 200 .mu.m, wherein the glass microfibers are
directionally oriented within the elastomer composition.
2. The elastomer composition of claim 1, wherein the average length
of the glass microfibers is between 5 and 100 .mu.m.
3. The elastomer composition of claim 2, wherein the average length
of the glass microfibers is between about 10 and 70 .mu.m.
4. The elastomer composition of claim 1, wherein a glass microfiber
loading is between about 0.5 and 50 pounds per hundred of the
elastomer.
5. The elastomer composition of claim 4, wherein the glass
microfiber loading is between about 2 and 20 pounds per hundred of
the elastomer.
6. The elastomer composition of claim 1, wherein the average
diameter of the microfibers is between about 0.2 and 1 .mu.m.
7. The elastomer composition of claim 6, wherein the average
diameter of the microfibers is between about 0.3 and 0.8 .mu.m.
8. The elastomer composition of claim 1, wherein the glass
microfibers are silane-modified.
9. The elastomer composition of claim 8, wherein the glass
microfibers are silane-pretreated.
10. A tire, comprising: a tread, the tread comprising the elastomer
composition of claim 1.
11. The tire of claim 10, wherein the glass microfibers are
oriented substantially circumferentially.
12. The tire of claim 10, wherein the microfibers are oriented
substantially in a tread thickness orientation.
13. The tire of claim 10, wherein the microfibers are oriented
substantially laterally.
14. The tire of claim 10, wherein the microfibers are oriented
substantially 45.degree. in a plane formed between the tread
thickness and circumferential orientations.
15. The tire of claim 10, wherein the average diameter of the glass
microfibers is between about 0.2 and 1 .mu.m.
16. The tire of claim 10, wherein the glass microfibers are
silane-modified.
17. A tire, comprising: a sidewall, the sidewall comprising a
support member, the support member comprising the elastomer
composition of claim 1.
18. The tire of claim 17, wherein the glass microfibers are
oriented substantially circumferentially.
19. The tire of claim 17, wherein the glass microfibers are
oriented substantially in a sidewall thickness direction.
20. The tire of claim 17, wherein the average diameter of the glass
microfibers is between about 0.2 and 1 .mu.m.
Description
[0001] This application is a continuation of International
Application No. PCT/US06/34065, filed Aug. 31, 2006.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to elastomeric compositions
and more specifically, to elastomeric compositions containing
oriented glass microfibers and products made therefrom.
[0004] 2. Description of the Related Art
[0005] Efforts continue in the tire industry to improve tire
performance, especially in such areas as rolling resistance,
durability and the ability of a tire to operate in a run-flat mode
over an extended distance. Materials that are used in the tire as
well as the tire construction are both important factors in
achieving such improvements in tire performance. The materials
undergoing research in the tire industry include rubber
compositions having glass fibers incorporated into the blend.
[0006] The addition of fibers into a rubber composition is well
known. For example, in European Patent Application EP 0 719 820,
published Jul. 3, 1996, a rubber composition was disclosed as being
suitable for use in the tread of tires. The disclosed rubber
composition reportedly provided excellent rolling characteristics,
abrasion resistance, and improved dimensional stability and further
did not undergo excessive shrinkage when extruded into rubber
sheets for treads. The rubber composition included silica as a
reinforcing material to provide the improved rolling
characteristics and dimensional stability. Organic fibers, e.g.,
nylon, aramid, polyester, rayon or cotton, were added to the rubber
composition to limit the shrinkage of the resulting extruded rubber
sheets made from the disclosed composition.
[0007] In U.S. Patent Application No. 2004/0035515, published Feb.
26, 2004, a studless tire was disclosed having a tread with fibers
oriented in the tread-depth direction. These fibers, which could be
either organic or inorganic fibers, had a Mohs hardness of 3 to 7
because fibers with a Mohs hardness of less than 3 are softer than
ice so that the road scratching effect is insufficient and fibers
with a Mohs hardness of more than 7 becomes harder than asphalt
causing the road to shave. Examples of such materials were
disclosed having glass fibers with an average fiber diameter of 33
.mu.m and of 200 .mu.m.
[0008] In U.S. Pat. No. 4,048,137, issued Sep. 13, 1977, an
elastomeric material was disclosed that was reinforced with short
small diameter insulating glass fibers. The glass fibers were
disclosed as being treated with a silane coupling agent and further
having lengths of between 3 to 50 mm and diameters of between 0.5
and 3.8 .mu.m, preferably between 2.5 and 3.8 .mu.m. It was
disclosed that such glass fibers provide excellent reinforcement to
elastomers.
[0009] In U.S. Pat. No. 6,209,604, issued Apr. 3, 2001, a pneumatic
tire for passenger vehicles was disclosed having at least one sheet
of a rubber-filament fiber composite in the sidewall. The fibers
useful for the invention were disclosed as being both inorganic and
organic fibers having diameters of between 0.0001 and 0.1 mm and
having a length greater than at least 8 mm. The elastomer was
disclosed as being applied to the non-woven fiber fabric having a
thickness of between 0.05 mm and 2.0 mm.
[0010] In U.S. Pat. No. 6,631,748, issued Oct. 14, 2003, a
pneumatic passenger tire suitable for use under run-flat conditions
is disclosed having a sidewall insert. The sidewall insert is
disclosed as having short fibers within the insert to provide
additional rigidity to the sidewall. Suitable fibers are disclosed
as being organic fibers such as rayon, nylon, polyester or aramid.
It is further disclosed that the fibers may be positioned radially
or at a bias but specifically not placed in a circumferential
orientation.
[0011] As with many properties associated with tires, the change of
one material or construction of a tire to improve one physical
characteristic of the tire often results in the decrease of other
physical characteristics of the tire. What are needed are materials
that improve at least one tire characteristic while still providing
a favorable mix of other physical characteristics.
SUMMARY OF THE INVENTION
[0012] The present invention provides elastomer compositions and
products formed from the elastomer compositions. In a particular
embodiment of the elastomer composition, the composition includes
an elastomer selected from one or more natural rubbers, one or more
synthetic rubbers or combinations thereof and glass microfibers
having an average fiber diameter of no more than about 5 .mu.m and
an average length of between about 5 and 200 .mu.m, wherein the
glass microfibers are directionally oriented within the elastomer
composition. As known to those having ordinary skill in the art,
microfibers may be directionally oriented in a rubber composition
by processing the rubber composition containing the microfibers
through and extrusion or calendering process. Fibers oriented
through such a process are substantially oriented.
[0013] Embodiments of the present invention may include elastomer
compositions having glass microfibers that are silane-modified or
silane-pretreated.
[0014] In particular embodiments of the elastomer composition, the
average length of the glass microfibers may be between 5 and 100
.mu.m or in other embodiments, between about 10 and 70 .mu.m. The
glass loading may range between about 0.5 and 50 pounds per hundred
of the elastomer (phr).
[0015] Embodiments of the present invention may include glass
microfibers having an average diameter of between about 0.2 and 1
.mu.m or even between about 0.3 and 0.8 .mu.m.
[0016] Any of the elastomer compositions disclosed above or
otherwise an embodiment of the present invention may be used to
form a tire tread. Embodiments of the present invention that
include a tread for a tire may include glass microfibers that are
oriented substantially circumferentially or that are oriented
substantially in a tread thickness orientation. Other embodiments
may include glass microfibers that are oriented substantially
45.degree. in a plane formed between the tread thickness and
circumferential orientations.
[0017] Any of the elastomer composition disclosed above or
otherwise an embodiment of the present invention may be used to
form a support member within the sidewall of a tire. Embodiments of
the present invention that include a support member within the
sidewall of a tire may include microfibers that are oriented
substantially circumferentially or in a sidewall thickness
direction.
[0018] Of course the microfibers may be aligned substantially in
any direction that would provide desired physical characteristics
for any material, product or product component of the present
invention.
[0019] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of a preferred embodiment of the invention, as
illustrated in the accompanying drawing wherein like reference
numbers represent like parts of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIGS. 1A-1C are perspective views of calendered or extruded
skims of a rubber composition that illustrate a method for
orienting substantially unidirectionally the glass microfibers
therein.
[0021] FIG. 2 is a perspective view of a tread for a vehicle tire
illustrating the coordinate system for orienting the microfibers
therein.
[0022] FIG. 3 is a cross-sectional view of one-half of an uncured
run-flat tire illustrating the coordinate system for orienting the
microfibers in the sidewall according to the present invention.
[0023] FIG. 4 is a cross-sectional view of skims used to produce a
crescent shaped reinforcing member that is part of a sidewall of a
tire.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0024] The present invention provides elastomer compositions and
products made therefrom that surprisingly provide a combination of
favorable rigidity, hysteresis and elongation properties. These
properties are obtained by mixing very short (<200 .mu.m)
silane-pretreated glass microfibers into the elastomer composition
at a loading of between 0.5 and 50 pounds per hundred pounds of
elastomer (phr) in the composition. Importantly, the microfibers
are substantially oriented unidirectionally to obtain the
surprising combination of favorable rigidity, hysteresis and
elongation properties. Advantageously, the orientation of the
fibers provides an anisotropic material with improved rigidity in
the direction of the fiber orientation but with little or no change
in the physical properties in a direction orthogonal to the
orientation direction. Surprisingly, even with the large increase
in rigidity, the change in the hysteresis and elongation properties
is relatively small by comparison, thereby providing the favorable
mix of rigidity, hysteresis and elongation properties.
[0025] Suitable elastomers that may be used in the elastomer
composition of the present invention include, for example, one or
more natural rubbers, one or more synthetic rubbers or combinations
thereof. Synthetic rubbers may include, without limitation,
styrene-butadiene rubbers, nitrile-butadiene rubbers, butyl
rubbers, polyisoprenes, polybutadienes and ethylene propylene
terpolymers. The synthetic rubbers may include, but are not limited
to, polymers, e.g., homopolymers, copolymers, and terpolymers, that
are manufactured from 1, 3 butadiene, styrene, isoprene,
isobutylene, 2,3-dimethyl-1,3 butadiene, acrylonitrile, ethylene,
propylene, and the like.
[0026] Particular embodiments of the elastomer composition may
include other components such as, for example, curing agents,
reinforcing fillers, coupling agents, plasticizers, antiozonants,
resins, various processing aids, oil extenders, antidegradents,
antioxidants or combinations thereof as known to those having
ordinary skill in the art. Curing agents that may be included in
the elastomer composition include, for example, sulfur, sulfur
donors, activators, accelerators, peroxides, and other systems used
to effect vulcanization of the elastomer composition. Fillers may
include, for example, carbon black, silica, clay and combinations
thereof.
[0027] The glass microfibers that are included in the elastomer
composition may be obtained either as a wool product, which is
typically made up of fibers that are random in length, or as a
chopped strand product, which is typically comprised of continuous
strands chopped at fixed lengths. Either of these types of products
is suitable for use in accordance with the present invention. It
should be noted that during processing of the elastomer
composition, the glass wool and the elastomer may be added to a
banbury mixer for mixing, which breaks up the glass wool into
suitable lengths of the microfibers. Suitable glass microfibers may
be obtained from Lauscha Fiber International of Germany with
manufacturing facilities in Summerville, S.C., under several
different product names including, for example, B-04-F. While the
glass chemical composition may vary for different applications, a
suitable glass composition for the glass includes the
"borosilicate" glass microfibers that are available from Lauscha
Fiber International.
[0028] Suitable useful glass microfibers include, but are not
limited to, those microfibers having an average diameter of less
than about 5 .mu.m. Particular embodiments of the present invention
include glass microfibers in the elastomer composition that have an
average fiber diameter less than about 4 .mu.m and others less than
about 3 .mu.m. Other embodiments include glass microfibers having
an average diameter of between about 0.1 .mu.m and about 2 .mu.m
while other embodiments include fibers having an average fiber
diameter of between about 0.2 and 1 .mu.m. Other embodiments
include glass microfibers having an average fiber diameter of
between about 0.3 and about 0.8 .mu.m.
[0029] Preferably, though not limiting the invention, the average
length of the microfibers in the elastomer composition is less than
about 200 .mu.m. As the microfibers are mixed with the elastomer in
the banbury mixer, the brittle glass microfibers are broken down to
the desired length. Particular embodiments of the elastomer
composition include microfibers having an average length of between
about 5 and 200 .mu.m while other embodiments include glass
microfibers having an average length of between about 5 and 100
.mu.m or of between about 10 and 70 .mu.m. In particular
embodiments of the present invention, the length to diameter (L/D)
ratio of the glass microfibers may range between about 30 and 500
while in other embodiments, the L/D may range between about 50 and
about 200.
[0030] Particular embodiments of the present invention include
adding the glass microfibers to the elastomer composition at a
loading of between about 0.5 and 50 pounds per hundred pounds of
elastomer (phr). Other embodiments include loadings of between
about 1 and 30 phr and others between about 2 and 20 phr.
[0031] Though not meant to limit the invention, it is thought that
the very short glass microfibers included in the elastomer
composition of the present invention provide the surprising results
of a favorable mix of the physical properties of rigidity,
hysteresis and elongation because the glass is brittle and avoids
clumping in the elastomeric composition as is often the case with
organic fibers. Furthermore, glass microfibers are easily treated
with coupling agents to make the fibers bond with the elastomeric
matrix. Using glass microfibers within the elastomer composition is
further beneficial because the small diameter mitigates the
penalizing effects of fiber in a composition, e.g., durability
(fatigue) and wear resistance (cohesion).
[0032] While oriented microfibers of other materials will increase
the rigidity of an elastomeric composition, these other materials
trade off the gain in rigidity with significantly poorer elongation
and/or hysteresis physical properties. This is true of other
materials even when the other materials are formed into very short
(<200 .mu.m) lengths and added into elastomer compositions. It
is the very short silane-treated glass microfibers that provide the
surprising results of an elastomer composition having increased
rigidity while maintaining a favorable mix of both elongation and
hysteresis physical properties.
[0033] Treating the microfibers with a silane coupling agent is
desirable to minimize the hysteresis of the elastomer composition.
It is believed, but not meant to limit the invention, that
providing improved bonding between the elastomer and the glass
microfibers in the elastomer composition provides a lower
hysteresis of the elastomer composition.
[0034] Pretreating glass fibers with a silane coupling agent is
well-known to those having ordinary skill in the art. One or more
coupling agents may be used in the elastomeric compositions of the
present invention. The coupling agent may be a bifunctional
organosilane cross-linking agent. By an "organosilane cross-linking
agent" is meant any silane coupled filler and/or cross linking
activator and/or silane reinforcing agent known to those skilled in
the art including, but not limited to, vinyl triethoxysilane,
vinyl-tris-(beta-methoxyethoxy)silane,
methacryloylpropyltrimethoxysilane, gamma-amino-propyl
triethoxysilane, gamma-mercaptopropyltrimethoxysilane and the like,
and mixtures thereof. In a preferred embodiment, the organosilane
cross-linking agent is selected from the group consisting of
bis-(3(triethoxysilyl)-propyl)-tetrasulfane (TESPT) (sold
commercially as "Si69" by Degussa),
gamma-mercaptopropyltrimethoxysilane (sold commercially as "Si189"
by Degussa), and 3-thiocyanatopropyl-triethoxy silane (sold
commercially as "Si264" by Degussa).
[0035] The process employed to pretreat the glass microfibers is
neither sophisticated nor novel. The steps of the process include
preparing a silane solution, dipping the microfibers into the
solution, and then drying the fibers to remove the carrier solvent.
In one procedure, a silane solution was prepared as a 5.8 wt. %
solution of TESPT in ethanol. The fiber wool was treated by dipping
the fibers in the solution. Good wet-out of the fibers was ensured
by wringing the fiber wool, which removed air bubbles and forced
the wet-out from the glass wool. The fibers were then dried at
about 105.degree. C.
[0036] As noted above, though not preferred, the coupling agent may
be added to the banbury mixer with untreated glass microfibers to
treat the fibers in situ during the mixing process. Such a process,
as well as the pretreatment described above, provides
silane-modified glass microfibers. Other methods for modifying the
glass microfibers with silane may be known or devised by those
having ordinary skill in the art. A preferred coupling agent
suitable for such use and known to those having ordinary skill in
the art is bis-(3(triethoxysilyl)-propyl)-tetrasulfane carried on
N330 carbon black at a 1:1 ratio by weight. Optionally, any
coupling agent such as those disclosed above may be added to the
banbury mixer with the pretreated glass microfibers to treat the
exposed untreated ends of the shattered microfibers.
[0037] The glass microfibers are oriented substantially
unidirectionally to procure the surprising physical characteristics
of the present invention. While any process may be used to orient
the glass microfibers, known methods include orienting microfibers
through an extrusion or calendering process. Calendering processes
include those that utilize rollers to press the mixed elastomer
composition into thin sheets or skims. Extrusion processes include
those that utilize force to push the rubber composition through a
die to form a shaped product.
[0038] Of these two types of processes, calendering provides
superior orientation of the glass microfibers in a substantially
unidirectional orientation. The anisotropic ratio, which is the
ratio of a physical property, e.g., modulus, measured in the
direction of the microfiber orientation to that measured
orthogonally, provides a measurement of the degree of orientation
of the fibers. For example, in one set of measurements of an
elastomer composition in accordance with the present invention, the
anisotropic ratio of the tensile moduli at 10% was 1.3 in an
extruded sample and 1.7 in a calendered sample. The higher
anisotropic ratio for the calendered sample evidences that the
calendered material possesses superior orientation of the glass
microfibers in a substantially unidirectional orientation when
compared to the extruded material.
[0039] FIGS. 1A-1C are perspective views of calendered or extruded
skims of a rubber composition that illustrate a method for
orienting glass microfibers substantially unidirectionally therein.
FIG. 1A illustrates orientation of the microfibers in the direction
of the skim (X direction) or in the direction orthogonal to the X
direction (Y direction). A skim 1 is produced through a roller
process that substantially orients the glass microfibers 2 in the X
direction. If a skim is desired having glass microfibers
substantially oriented in the X direction, then the process is
complete at this point. However, if the glass microfibers are to be
oriented in the Y direction, then the skim 1 is cut 3 into sections
4 that are then rotated 90 degrees so that the glass microfibers 2
are substantially oriented in the Y direction. The sections 4 may
then be bonded together at a seam 5. A plurality of skims 1 may be
stacked (not shown) to provide a desired thickness of elastomer
composition having glass microfibers oriented unidirectionally.
Each skim may be of any desired thickness but the thinner the skim,
the better the unidirectional orientation of the glass
microfibers.
[0040] FIG. 1B illustrates orientation of the glass microfibers in
a generally Z direction, which is a direction orthogonal to both
the X and Y directions shown in FIG. 1A. The rollers 6 on the
calendar produce the calendered skim 1 from the elastomeric
composition 2 fed into the rollers 6. The glass microfibers 2 are
aligned, as shown in FIG. 1A, in the X direction as the skim is
produced off the rollers 6. However, by repeatedly folding 8 the
calendered skim 1, the glass microfibers 2 are aligned in the Z
direction.
[0041] FIG. 1C illustrates orientation of glass microfibers in a
generally 45.degree. orientation from the calendered or extruded
direction X. A stack 10 of calendered skims 1 is cut 11 at a
45.degree. angle. Each of the cut sections 12 are separated and
then rotated 90 degrees. The rotated sections 16 then have the
microfibers 2 contained therein substantially oriented
unidirectionally at 45.degree.. The sections 16 may then bonded
together at a seam 18.
[0042] The elastomer composition disclosed herein may be used for
various elastomeric products such as a tread compound, undertread
compound, sidewall compound, wire skim compound, inner liner
compound, bead, apex, any compound used in a tire carcass and other
components for vehicle tires, industrial rubber products, seals,
timing belts, power transmission belting, and other rubber goods.
As such, the present invention includes products made from the
elastomer composition disclosed herein. The elastomer composition
of the present invention would be especially beneficial for those
applications requiring materials with higher rigidity while
maintaining favorable hysteresis and elongation physical
properties.
[0043] Particular embodiments of the present invention include tire
treads for vehicle tires. Particular embodiments of the present
invention include treads for both passenger and truck tires. These
treads are formed of the elastomer composition having the very
short silane-pretreated glass microfibers that are oriented
substantially unidirectionally within the composition. The treads
may be bonded or otherwise made an integral part of the vehicle
tire by methods known by those having ordinary skill in the art and
such methods or processes are not a part of the present
invention.
[0044] Orienting the glass microfibers substantially
unidirectionally in the tread greatly improves the rigidity of the
tread while, surprisingly, having a minimum impact on hysteresis,
thereby decreasing the rolling resistance of the tire and retaining
acceptable endurance properties.
[0045] The direction of the fiber orientation influences the
physical properties of a tire tread of the present invention. FIG.
2 is a perspective view of a tread for a vehicle illustrating the
coordinate system for orienting the microfibers in the tread.
Microfibers oriented in the X direction are oriented
circumferentially around the tire tread 35. Microfibers oriented in
the thickness direction of the tread 35 are oriented in the radial,
or Z direction. Microfibers oriented orthogonally to both the X
direction and the Z direction are oriented in the lateral, or Y
direction, across the tread from side to side. As noted in FIG. 2,
the microfibers may also be oriented in a +45.degree. 33 or a
-45.degree. 32 orientation in the X-Z plane. Additionally, the
microfibers may be oriented in a 45.degree. 31 orientation in the
X-Y plane. Of course, any desired orientation of the fibers may be
achieved and the invention is not meant to be limited only to those
fiber orientations illustrated in FIG. 2.
[0046] As noted above, the direction of the orientation of the
glass microfibers impacts the physical characteristics of a tread
made in accordance to the present invention. While the preferred
orientation of the fibers may depend on a particular application or
method of making or assembling a final product, in particular
embodiments of a tire tread according to the present invention,
orienting the microfibers in the tread thickness direction provides
the greatest improvements in the rolling resistance while
microfibers arranged in the +45.degree. orientation provide the
greatest wear resistance.
[0047] Particular embodiments of the present invention further
include sidewall supports for vehicle tires, especially for those
tires that are suitable for run-flat operation. As known to those
having ordinary skill in the art, run-flat tires are designed to
operate for a suitable distance after loss of normal inflation
pressure. Sidewall supports are formed of the elastomer composition
having the silane-pretreated glass microfibers that are oriented
substantially. The supports are made a part of the sidewall by tire
building methods known to those having ordinary skill in the art
and such methods or processes are not a part of the present
invention.
[0048] FIG. 3 is a cross-sectional view of one-half of an uncured
run-flat tire having a sidewall support in accordance with the
present invention. The run-flat tire 60 includes a crown portion 61
with a tread 62 and a tread reinforcing package 63. The run-flat
tire 60 further includes a sidewall 70 having a crescent shaped
reinforcing member 64 with a supportive complex 65 and a protective
complex 66. An inner liner 67 and tire carcass 68 wrapped around a
bead core 69 are also included as typical in a pneumatic vehicle
tire. Microfibers may be oriented in the support sections of the
sidewall 64 such as, for example, the crescent shaped reinforcing
member 64. Microfibers oriented circumferentially around the
sidewall 64 of the tire 60 are oriented in the X direction.
Microfibers oriented in a sidewall thickness direction are oriented
in the Z direction. Microfibers oriented orthogonally to both the X
direction and the Z direction are oriented in the Y direction. Of
course, any desired orientation of the fibers may be achieved and
the invention is not meant to be limited only to those fiber
orientations illustrated in FIG. 3A.
[0049] FIG. 4 is a cross-sectional view of skims used to produce a
crescent shaped reinforcing member 64 that is part of a sidewall of
a tire. In this particular embodiment, the skims 71 are produced by
the calendering process shown in FIGS. 1A-1C so that the fibers 2
are aligned in the thickness direction of the crescent shaped
reinforcing member 64. The skims 71 are stacked during the assembly
process to form the reinforcing member 64. When the reinforcing
member 64 is made a part of the sidewall 64, the reinforcing member
64 assumes the shape of the sidewall 64, as shown in FIG. 3A.
Changing the shape of the reinforcing member 64 to the shape of the
sidewall 64 changes the apparent orientation of the fibers 2
relative to the sidewall 64 although the microfibers 2 remain
substantially orthogonal to the base 72 of each of the skims 71
making up the reinforcing member 64.
[0050] The physical characteristics of the elastomer composition of
the present invention provide the benefits that are sought in
run-flat tire applications. Because a run-flat tire must operate
over a significant distance in a non-inflated state while still
providing support for a vehicle, rigidity and hysteresis properties
of the materials making up the sidewall are critical. Rigidity is
required to provide the needed support for the vehicle or load on
the tire and low hysteresis is needed to minimize heat buildup in
the tire during run-flat operation. Surprisingly, a sidewall
comprising the elastomer composition of the present invention
provides the desired mix of rigidity, hysteresis and tensile
strength/elongation physical properties.
[0051] The invention is further illustrated by the following
examples, which are to be regarded only as illustrations and not
delimitative of the invention in any way. The properties of the
compositions disclosed in the examples are evaluated as described
below.
[0052] Moduli of elongation (MPa) are measured at 10% and at 100%
at a temperature of 23.degree. C. in accordance with ASTM Standard
D412 on ASTM C test pieces. These measurements are true secant
moduli in MPa, that is to say the secant moduli calculated reduced
to the real cross-section of the test piece at the given
elongation.
[0053] Hysteresis losses (HL) are measured in percent by rebound at
60.degree. C. at the sixth impact in accordance with the following
equation:
HL (%)=100(W.sub.0-W.sub.1)/W.sub.1,
where W.sub.0 is the energy supplied and W.sub.1 is the energy
restored.
[0054] The elongation property is measured as elongation at break
(%), which is measured at 23.degree. C. in accordance with ASTM
Standard D412 on ASTM C test pieces.
Example 1
[0055] This example compares physical properties of exemplary
elastomer compositions having glass microfibers with other
elastomer compositions having microfibers made of other materials,
namely, carbon microfibers and KEVLAR pulp microfibers. The
properties of these fibers are shown in Table 1. The KEVLAR pulp is
available from Dupont, the glass microfibers from Lauscha Fiber
International and the PYROGRAF carbon fibers from Pyrograph
Products, Inc. of Cedarville, Ohio. It should be noted that all of
the fibers tested were microfibers having an average diameter of no
more than 5 .mu.m and an average length of no more than 50
.mu.m.
TABLE-US-00001 TABLE 1 Microfiber Properties Diameter, Length,
Surface Fiber .mu.m .mu.m L/D Area, m.sup.2/g Glass, B-00-F 0.32
<50 <600 4.95 Glass, B-04-F 0.45 <400 3-4 Glass, B-50-R 5
<40 0.32 KEVLAR Pulp <3 <5 >3 8 Carbon PYROGRAF III
0.1-0.2 <100 <1000 10-30
[0056] Elastomer formulations were prepared by mixing the
components given in liable 2, except for the sulfur and the curing
agents, in a banbury mixer operating at 55-65 RPM until a
temperature of between 155 and 170.degree. C. was reached. The
sulfur and curing agents were then added on a roll mill.
Vulcanization was effected at 150.degree. C. for 25 minutes. The
formulations were then tested to measure their physical
properties.
[0057] The compositions of the formulations are shown in Table 2 as
the weight percent of elastomer content. Each of the formulations
included a mixture of natural rubber and butadiene rubber. The
materials listed as "other" included antioxidants, antiozonants,
plasticizers, sulfur and curing agents such as accelerators,
retarders and activators as known to those having ordinary skill in
the art. The silane coupling agent
bis-(3(triethoxysilyl)-propyl)-tetrasulfane (TESPT) was added to
some of the compositions having the glass microfibers. Table 2
further provides the results of the analyses of the physical
properties of the formulation.
TABLE-US-00002 TABLE 2 Physical Properties of Elastomers Having
Different Fiber Types (Normalized) Glass, 0.4 .mu.m Glass 5 .mu.m
Carbon KEVLAR Fiber Loading 0 5 10 10 10PT 10 20 0 10 15.7 0 2 3
Natural Rubber 80 80 80 80 80 80 80 80 80 80 50 50 50 Butadiene
Rubber 20 20 20 20 20 20 20 20 20 20 50 50 50 Carbon Black 35 35 35
35 35 35 35 39 39 39 55 55 55 TESPT 1 0.5 0.5 0.5 1 Other 12 12 12
12 12 12 12 20 20 20 32 32 32 Modulus 10% X 100 138 166 191 175 150
184 100 215 275 100 152 248 Modulus 10% Y 97 106 106 113 113 106
119 96 132 158 103 126 132 Anis X/Y 1.0 1.3 1.6 1.7 1.6 1.4 1.6 1.0
1.6 1.7 1.0 1.2 1.9 HL X 100 146 166 146 117 127 131 100 116 122
100 141 173 HL Y 99 118 123 118 108 108 110 100 112 122 Elong Brk %
X 100 93 95 88 76 89 84 100 52 38 100 84 74 Elong Brk % Y 103 96 98
91 78 92 87 107 78 62
[0058] As the physical characteristics demonstrate in Table 2, the
glass microfibers that were pretreated with silane (designated PT
in the fiber loading row of Table 2) had the best mix of rigidity,
hysteresis and elongation characteristics. While the carbon
microfibers provided a good increase in rigidity with minimal
impact on hysteresis, the carbon microfibers provided a huge
negative impact on the elongation property. Furthermore, while the
KEVLAR microfibers provided a good increase in rigidity with
minimum impact on elongation, the KEVLAR microfibers provided a
huge negative impact on hysteresis. Only the pretreated glass
microfibers provided the surprising result of a favorable mix of
rigidity, hysteresis and elongation properties.
Example 2
[0059] This example demonstrates the effectiveness of an elastomer
composition that includes very short silane-pretreated glass
microfibers used in a sidewall reinforcement member for a run-flat
tire. Elastomer formulations were prepared by mixing the components
given in Table 3, except for the sulfur and the curing agents, in a
banbury mixer operating at 55-65 RPM until a temperature of between
155 and 170.degree. C. was reached. The sulfur and curing agents
were then added on a roll mill. Vulcanization was effected at
150.degree. C. for 25 minutes. The formulations were then tested to
measure their physical properties. The glass microfiber was
pretreated with a silane coupler (TESPT) as previously
described.
[0060] The compositions of the formulations are shown in Table 3 as
the weight percent of elastomer content. Each of the formulations
included a mixture of natural rubber and polybutadiene rubber. The
materials listed as "other" included antioxidants, antiozonants,
plasticizers, sulfur, resins and curing agents such as
accelerators, retarders and activators as known to those having
ordinary skill in the art. Table 3 further provides the results of
the analyses of the physical properties of the formulations.
TABLE-US-00003 TABLE 3 Physical Properties of Elastomers with Glass
Microfibers (Normalized) Extruded Calendered Formulation 1 2 3 4 5
Microfiber Loading, B-04-F 0 10 20 10 20 Natural Rubber 80 80 80 80
80 Polybutadiene Rubber 20 20 20 20 20 Carbon Black 35 35 35 35 35
Silica 15 15 15 15 15 Other 22.2 22.2 22.2 22.2 22.2 Modulus 10% X
100 156 241 219 328 Modulus 10% Y 100 119 139 118 135 Anis X/Y 1.0
1.3 1.7 1.9 2.4 HL X 100 104 111 117 123 HL Y 96 97 98 105 109
Elong Brk % X 100 88 83 85 81 Elong Brk % Y 91 71 61 68 78
TABLE-US-00004 TABLE 4 Tire Test Results Using Formulations of
Table 3 (Normalized) Formulation Tire Data (255/50/R17) 1 2 3 4 5
Inflated Rolling Resistance 100 103 104 105 106 ISO 16992 Run-Flat
Endurance 100 106 125 -- 193 On-Vehicle Run-Flat Endurance 100 138
153 -- 119
[0061] As the physical properties shown in Table 3 demonstrate, the
calendered elastomeric composition provided a large increase in
modulus while surprisingly maintaining a good mix of hysteresis and
elongation characteristics.
[0062] Tires were made having dimensions of 255/50/R17. The
crescent shaped reinforcing member in the sidewall of the tires was
constructed of skim layers (formed by either calendering or
extrusion) with the fibers oriented circumferentially. The
calendered layers were made of the elastomeric compositions shown
in Table 3.
[0063] The tires having the crescent shaped reinforcement member
were tested for inflated rolling resistance, for run-flat endurance
under the ISO Standard 16992 and for on-vehicle run-flat endurance.
As the test results shown in Table 4 demonstrate, rolling
resistance (a function of hysteresis) advantageously improved by
about 3-6% (indicating a decrease in hysteresis) while the run-flat
endurance, as tested under the ISO Standard 16992, increased by
over 90 percent.
Example 3
[0064] This example demonstrates the effectiveness of an elastomer
composition that includes very short silane-pretreated glass
microfibers used in a tread on a truck tire. Elastomer formulations
were prepared by kneading the components given in Table 5, except
for the sulfur and the curing agents in a banbury mixer operating
at 55-65 RPM until a temperature of between 155 and 170.degree. C.
was reached. The sulfur and curing agents were then added on a roll
mill. Vulcanization was effected at 150.degree. C. for 25 minutes.
The formulations were then tested to measure their physical
properties. The glass microfiber was pretreated with a silane
coupler (TESPT) as previously described.
[0065] The compositions of the formulations are shown in Table 5 as
the weight percent of elastomer content. One of the groups of
formulation included only natural rubber while the second group of
formulations included natural rubber, butadiene rubber and
styrene-butadiene rubber. The materials listed as "other" included
antioxidants, antiozonants, plasticizers, sulfur, resins and curing
agents such as accelerators, retarders and activators as known to
those having ordinary skill in the art. Table 5 further provides
the results of the analyses of the physical properties of the
formulation.
TABLE-US-00005 TABLE 5 Physical Properties of Elastomers with Glass
Microfibers (Normalized) I II Formulation 1 2 3 4 Microfiber
Loading B-00 FST 0 10 Microfiber Loading B-04-FST 0 10 Natural
Rubber 100 100 15 15 Butadiene Rubber 15 15 Styrene-butadiene
rubber 70 70 Carbon Black 45 45 50 50 Silica TESPT 0 0.5 0 0.5
Reinforcing Resin 1.5 0 0 0 Other 11.4 11.4 11.4 11.4 Modulus 10% X
100 148 100 177 Modulus 10% Y 104 98 109 Anis X/Y 1.0 1.5 1.6 HL X
100 105 100 102 HL Y 104 96 100 Elong Brk % X 100 79 Elong Brk % Y
97 88 Tire Data Rolling Resistance Circumferential Orientation 100
102 100 105 Lateral Orientation 100 106 Tread Thickness Orientation
100 113 45 XZ Steer 100 101
[0066] Again, the addition of very short silane-pretreated glass
microfibers provided an elastomer composition having a large
increase in modulus while still maintaining a good mix of
hysteresis and elongation characteristics. Truck tires having
dimensions of 275/70R/22.5 were constructed with the tires having
treads formed of the elastomeric compositions shown in Table 4. The
treads all contained silane pretreated glass microfibers oriented
in either the circumferential, lateral, tread thickness or
45.degree. XZ plane (See, FIG. 2) direction.
[0067] As the results of the rolling resistance tests shown in
Table 4 demonstrate, the rolling resistance performance of the
tires actually improved (indicating lower hysteresis). The largest
improvement in rolling resistance was demonstrated when the
microfibers were arranged in the tread-thickness direction with an
improvement of 13%.
[0068] The terms "comprising," "including," and "having," as used
in the claims and specification herein, shall be considered as
indicating an open group that may include other elements not
specified. The term "consisting essentially of," as used in the
claims and specification herein, shall be considered as indicating
a partially open group that may include other elements not
specified, so long as those other elements do not materially alter
the basic and novel characteristics of the claimed invention. The
terms "a," "an," and the singular forms of words shall be taken to
include the plural form of the same words, such that the terms mean
that one or more of something is provided. The terms "at least one"
and "one or more" are used interchangeably. The term "one" or
"single" shall be used to indicate that one and only one of
something is intended. Similarly, other specific integer values,
such as "two," are used when a specific number of things is
intended. The terms "preferably," "preferred," "prefer,"
"optionally," "may," and similar terms are used to indicate that an
item, condition or step being referred to is an optional (not
required) feature of the invention.
[0069] It should be understood from the foregoing description that
various modifications and changes may be made in the preferred
embodiments of the present invention without departing from its
true spirit. The foregoing description is provided for the purpose
of illustration only and should not be construed in a limiting
sense. Only the language of the following claims should limit the
scope of this invention.
* * * * *